Such a double brake according to the invention is of the type comprising two rotor (or stator) bucket wheels that are arranged back to back, and which can be rotated together and also comprising two stator (or rotor) bucket wheels. The two sets of bucket wheels cooperate to form two toroidal working chambers which can be filled with working fluid. The buckets or blades of all four bucket wheels, viewed in cylindrical section, are all set at an angle in the same direction relative to the axis of rotation of the bucket wheels, so that in one rotary direction of the bucket wheels, only one of the working chambers is predominantly active, and in the other rotary direction, only the other working chamber is predominantly active. The brake also has a stationary shell, a common inlet line for both the working chambers, and has outlet ducts leading from the two working chambers.
Double fluid brakes of this kind can produce the same amount of braking moment in both rotary directions, which is necessary, for example, for railway vehicles.
Known double brakes of this kind are described in the following publications:
1. German Patent Specification No. 1,600,191.
2. German Laid-Open Patent Specification No. 1,755,818.
3. German Laid-Open Patent Specification No. 2,208,857.
4. German Laid-Open Patent Specification No. 2,211,379.
5. "Leichtbau der Verkehrsfahrzeuge". 1969, Pages 183 to 187.
In the above mentioned double brakes, either the two rotor bucket wheels or the two stator bucket wheels are arranged back to back in the center of the unit, and they are connected together to form a double bucket wheel. The two outer bucket wheels are connected together by a shell, which also surrounds the central double bucket wheel. Between the outer circumference of the central double bucket wheel and the shell there is an annular gap. The two working chambers of the double brake are interconnected through this gap.
Double brakes according to publications 1 and 2 have the drawback that the high fluid pressure prevailing in the radially outer region of the working chamber which is then active penetrates, via the annular gap, into the radially outer region of the working chamber which is then inactive at the time, and into the inlet line. This means that a filling pump that supplies working fluid has to work against undesirably high pressure. It has been proposed to overcome this disadvantage by arranging labyrinth seals in the above described annular gap (see publication 5 above, FIGS. 8 and 9). Although the transmission of pressure into the inactive working chamber can be obstructed by these means, it cannot be prevented completely. The filling pump, therefore, still requires a relatively high input. In addition, separate outlet ducts have to be provided, each with an overflow valve to serve as a control device (see publication 5 above, FIG. 12). A better result can be achieved with another known double brake (see publication 3 above) by giving each working chamber a separate inlet line with a non-return valve. In this way, the high pressure can only enter the inactive working chamber and can no longer penetrate into the inlet duct. The filling pressure required is quite low in this case, and a common outlet duct can also again be provided for both of the working chambers.
However, a disadvantage of this construction is that the separate inlet ducts take up a relatively large amount of space. As a result, this known brake cannot be used if only a small amount of space can be made available for a hydrodynamic brake, for example in a drive unit for a vehicle.
It is also known from publications 3 and 5 above to arrange the inlet ducts for the working chambers in the rotor bucket wheels (pump effect) instead of in the stator bucket wheels. This arrangement also means that the working fluid for the brakes can be supplied at a relatively low filling pressure.